Certain aircraft propulsors may drive a variable-frequency generator (VFG) for providing electrical power to the aircraft. Such a VFG may be coupled to an engine core of the aircraft propulsor through a direct drive gear train, where the direct drive gear train may have a damping factor typically no greater than about 0.02, or 2%. Because of this low damping factor, torsional oscillation may arise within the gear train in the form of limit cycle behavior through oscillation at one or more natural (e.g., resonant) frequencies. Torsional oscillations at such frequencies may be amplified by feedback control, leading to sustained torsional oscillation (STO), also known as sub-synchronous oscillation (SSRO).
Such torsional oscillations may cause a reduction in quality of the electrical power generated by the VFG. In particular, the torsional oscillations may result in the electrical power exhibiting oscillations in voltage and/or current associated with one or more natural frequencies of the gear train. Such oscillations may thus introduce undesirable noise into the electrical power provided to the aircraft which, if left uncorrected, may cause excessive wear and/or damage to aircraft electrical systems.